Process of coating



Patented Sept. 11, 1923..

EABZLE E. SCHUMACHER, OF EAST ORANGE, NEW JERSEY, ASSIGNOR '.l0 WESTERNELECTRIC COMPANY, INCORPORATED, 013 NEW YORK, N. Y., A CORPORATION OF"\NEW xoax.

PROCESS OF COATING .80 Drawing.

To all whom it may concern:

Be itknown. that I, EARLE E. SCHU- tain new and useful Improvements inProcesses. of Coatingyof which the following is a full, clear, concise,and exact description.

i This invention relates to electron dlscharge devices and pertainsespecially to the manufacture of thermionic cathodes therefor.

The object of this invention is'a processv of coating alkalineearthoxides on a core of oxidi'zable metal. P

This invention pr' vides for a coating of base metal cores wihthermionic material without an appreciable oxidation of the core.

The process of coating comprises the preparation of a'molten bath of analkaline earth compound or a mixture of alkaline earth compounds at amoderate temperature, and

the dipping of the material to an instant in this bath. The coatin isthus applied to the core in the absence 0 air and the oxidation of thesurface of the core is prevented. .WVhen the coating is heated it breaksdown into the alkaline earth oxides which are highly activethermionically.

In the preferred form of the invention a bath-of molten barium hydroxideor a mixture of barium hydroxide with strontium or a calcium hydroxideis prepared by mixing one or more of these substances in'suitable quan-.tities in a vesseland heating the same to a temperature from about/450to 750, degrees centigrade. At this term erature the substances havebecome melte in their water of crystallization and the material to becoated 40 is then merely dipped into this bath whereupon a firmlyadherent coating is formed on the surface of the metal. It is foundthat,

by this particular process, base metals may be coated with a firmcoating in the absence of air without the necessity of any electrolyt icaction.

In this method of dipping the filament in a bath of -molten hydroxide,it is probable that a very. small and negligible amount of thestable-compounds above mentioned are formed; yet, since the filamentisnot heated in the air, there is a large excess of uncombined alkalineearth oxides present in the e coated for Application filed niarch 19,1920. Serial No. 367,086.

coat and it'is to these uncombined oxides that the filament owes itsactivity.

A small amonnt'of oxidation of the'core is desirable in a 'di-ppingprocess in that it imparts a rou h surface to the metal to whichthe-alk: in'e earth oxides will adhere more firmly. This partialoxidation may be brought about by either of two'methods: the

filament may be oxidized by a previous heating in the air or, the bathmay be heated up to a temperature sufliciently high such as600cent1grade so that it becomes an oxi- 5 dizing 'medium in itself dueto the formationof a certain amount of barium eroxide.

By the above process thermionically active filaments havc'been made ofcores of iron, tungsten, molybdenum, carbon and alloys of chromium ortantalum with various combi' nations of the other metals.

What isclaimed isz r 1.-A process of coating which com rises dipping abase metal core to be coate in a molten bath of alkaline earthhydroxide.

* 2. A process of coating which comprises heating a quantity of alkalineearth hydroxide in a ,vessel to a temperature where it be comes meltedin its water of crystallization so and then dipping the material to becoated in the bath.

. 3. A process of coating which comprises heating abath of bariumhydroxide to a temperature from about, 450 to 750 centi- 85.

rade and then dipping a base metal core 1nto the bath.

4. .A process of coating which comprises. heating a mixture ofalkalineearth hydroxides to a temperature from about 450,to 750 centigrade andthen dipping a base metal core into the bath.

5. A process of coating which comprises dipping an electrode to becoated in a molten bath of alkaline earth hydroxide. I 6. Aprocess ofcoating which comprises dipping a filament to be coated in a molten bathof alkaline earth hydroxide.

7. 'A process of coatin which comprises heating an alkaline earthydroxide to a we term erature from about 450 to 750 centi gra e andthen dipping a base metal electrode therein.

In witness whereof, I hereunto subscribe myname this 10th day of March,A. D. 1920.

EARLE'E. SGHUMACI-IER.

